Wireless communication semiconductor integrated circuit device and wireless communication system

ABSTRACT

A receiving circuit of a direct conversion system which includes a differential amplifier circuit which amplifies a received signal, a mixer which combines the amplified received signal and an oscillation signal having a predetermined frequency to perform frequency conversion, and a high gain amplifier circuit in which programmable gain amplifiers and filters which eliminate noise of the received signal, are connected in a multistage and which is configured such that an amplification factor is varied according to the level of the received signal. In the receiving circuit, the low noise amplifier is brought to a non-operating state to allow execution of a DC offset cancel operation of the programmable gain amplifier on the pre-stage side of the high gain amplifier circuit. Thereafter, the low noise amplifier is brought to an operating state to allow execution of a DC offset cancel operation of the final-stage programmable gain amplifier.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation of application Ser. No.10/948,183, filed Sep. 24, 2004, which claims priority from Japanesepatent application No. 2003-342874 filed on Oct. 1, 2003, the content ofwhich is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a technique effective if applied to again programmable signal amplifier circuit, a received signal amplifiercircuit employed in a wireless communication system and a receivingcircuit which down-converts a high frequency received signal into asignal lying in an audio frequency band on a direct conversion systembasis, and to, for example, a technique effective suitable forapplication to a high frequency semiconductor integrated circuit device(hereinafter called high frequency IC) incorporating thereinprogrammable gain amplifiers that constitute a wireless communicationsystem, and a wireless communication system with the high frequencysemiconductor integrated circuit device built therein.

A high frequency IC having frequency conversion of transmit-receivesignals and a modem function has been used for recent cellular phones. Asuperheterodyne system which temporarily down-converts a received signalto an intermediate frequency signal and down-converts it to a signallying in an audio frequency band, and a direct conversion system whichdown-converts a received signal to a signal lying in an audio frequencyband are known for the conventional high frequency IC. The highfrequency IC of the direct conversion system is configured in such amanner that an LNA (Low Noise Amplifier) amplifies a received signal andthereafter a mixer combines the received signal and a local oscillationsignal, followed by being down-converted to a signal lying in an audiofrequency band, and a high gain amplifier circuit amplifies the weakreceived signal to about 1500 times at the maximum and passes it to abaseband LSI which performs its baseband processing.

The high gain amplifier circuit takes a configuration wherein since itamplifies the weak received signal while removing noise and a signalhaving an unnecessary frequency, low pass filters LPFs and programmablegain amplifiers (hereinafter abbreviated as PGAs) are alternatelyconnected in several stages. Incidentally, since an analog amplifiercircuit starting with PGA produces a DC offset due to variations inelement, etc., offset cancellation is essential.

As described above, the receiving circuit of the cellular phone usingthe plurality of PGAs has conventionally been provided with offsetcorrection circuits every PGA in general. The receiving circuit has beenconfigured so as to sequentially carry out offset cancellations in orderfrom the first-stage PGA to the subsequent-stage PGAs. Such offsetcancel operations of PGAs have been described in, for example, a patentdocument 1 (Japanese Unexamined Patent Publication No. 2003-152480).

SUMMARY OF THE INVENTION

Incidentally, although not described in the patent document 1, theoffset cancel operations of PGAs are carried out in a state in which apre-stage mixer is turned on and the LNA is turned off. The reason whythe mixer is turned on, is that since the mixer also has an offset, theoffset of the mixer and the offset of the first-stage PGA can becanceled out simultaneously when the mixer is held on upon the offsetcancellation of the first-stage PGA. The reason why the offsetcancellations of PGAs are performed in the turned-off state of the LNA,is that when the LNA is held on, a signal that leaks from a localoscillator is round-intruded into input terminals of the LNA via asemiconductor chip and a module substrate with the semiconductor chipmounted thereon, so that the mixer causes self-mixing, therebygenerating a DC offset, which in turn is amplified by a high gain PGAsection.

Meanwhile, the self-mixing due to the round intrusion of the localoscillation signal into the LNA input terminals can be reduced to someextent by using differential type circuits as the LNA and mixer andinphase noise cancel operations of the differential amplifiers. However,when pairing of the positive-phase and negative-phase sides of bothsingle-differential converters configured of baluns or the likeconnected between an antenna and the input terminals of the LNA, and afront end module is poor, the inphase noise round-intruded into theinput terminals of the LNA cannot be canceled sufficiently. Further,since module substrates each having a high frequency IC mounted thereonare different in structure, size and wiring pattern depending on users,the amount of leakage of the local oscillation signal round-intrudedinto the input terminals of the LNA varies too.

Therefore, the system for performing the offset cancellation of each PGAwhile the LNA remains off as described above is accompanied by theproblem that when the LNA is turned on after the completion of theoffset cancellation, the DC offset produced with self mixing due to theround intrusion of the local oscillation signal is amplified by the PGA.It has been revealed that although a shift in signal level due to such aDC offset has conventionally fallen within an allowable range, thedynamic range of an input to the baseband LSI also becomes narrow whenthe power supply voltage of the baseband LSI is lowered with a reductionin the voltage of a recent semiconductor integrated circuit, and hence adesired wave exceeds the dynamic range and is clipped even if the DCoffset developed with self mixing due to the round intrusion of thelocal oscillation signal is the same as conventional, thereby causing afear of degradation of reception sensitivity.

An object of the present invention is to provide a wirelesscommunication semiconductor integrated circuit device (high frequencyIC) of a direct conversion system, which is capable of canceling a DCoffset developed with self mixing of a mixer due to round intrusion of alocal oscillation signal into LNA input terminals and thereby improvingreception sensitivity.

Another object of the present invention is to provide a wirelesscommunication semiconductor integrated circuit device (high frequencyIC) of a direct conversion system, which causes no degradation ofreception sensitivity even if the dynamic range of an input to a circuitsupplied with an amplified received signal is narrow.

A further object of the present invention is to provide a wirelesscommunication semiconductor integrated circuit device (high frequencyIC) of a direct conversion system, which has stable receptionsensitivity without being affected by the characteristic of a mountedsubstrate.

The above, other objects and novel features of the present inventionwill become apparent from the description of the present specificationand the accompanying drawings.

Summaries of representative ones of the inventions disclosed in thepresent application will be explained in brief as follows:

A first invention of the present application provides a receivingcircuit of a direct conversion system, including a low noise amplifierwhich amplifies a differential received signal, a mixer which combinesthe amplified received signal and an oscillation signal having apredetermined frequency to thereby perform frequency conversion, and ahigh gain amplifier circuit in which a plurality of programmable gainamplifiers and a plurality of filters which eliminate noise of thereceived signal and an unnecessary wave, are connected in a multistageand which is configured such that an amplification factor is variedaccording to the level of the received signal, wherein the low noiseamplifier is brought to a non-operating state to thereby allow executionof an offset cancel operation of the corresponding programmable gainamplifier on the pre-stage side of the high gain amplifier circuit, andthereafter the low noise amplifier is brought to an operating state tothereby allow execution of an offset cancel operation of the final-stageprogrammable gain amplifier.

According to such means, even if a DC offset occurs with self mixing ofthe mixer due to round intrusion of a local oscillation signal into LNAinput terminals, the low noise amplifier is brought to the operatingstate to execute the offset cancel operation of the final-stageprogrammable gain amplifier, whereby offset cancellation can beperformed inclusive of the DC offset of the final-stage programmablegain amplifier and the DC offset produced with the self mixing of themixer.

Here, preferably, a register or control bit is provided which is capableof setting whether such a series of offset cancel operations that thelow noise amplifier is brought to the non-operating state to allow theexecution of the offset cancel operation of the programmable gainamplifier on the pre-stage side of the high gain amplifier circuit andthereafter the low noise amplifier is brought to the operating state toallow the execution of the offset cancel operation of the programmablegain amplifier of the final stage. Thus, such a system that the lownoise amplifier is brought to the operating state to allow the executionof the offset cancel operation of the final-stage programmable gainamplifier, thereby increasing the DC offset on the contrary is capableof avoiding selective execution of such an offset cancel operation byvirtue of the setting of the register.

A second invention of the present application provides a receivingcircuit of a direct conversion system, including a low noise amplifierwhich amplifies a differential received signal, a mixer which combinesthe amplified received signal and an oscillation signal having apredetermined frequency to thereby perform frequency conversion, and ahigh gain amplifier circuit in which a plurality of programmable gainamplifiers and a plurality of filters which eliminate noise of thereceived signal and an unnecessary wave, are connected in a multistageand which is configured such that an amplification factor is variedaccording to the level of the received signal, wherein when the highgain amplifier circuit is operated with high gain, the low noiseamplifier is brought to a non-operating state to allow execution of anoffset cancel operation of the programmable gain amplifier on thepre-stage side of the high gain amplifier circuit, and thereafter thelow noise amplifier is brought to an operating state to allow executionof an offset cancel operation of the final-stage programmable gainamplifier, and wherein when the high gain amplifier circuit is operatedwith low gain, the low noise amplifier is brought to the operating stateto execute in sequence the offset cancel operations of all programmablegain amplifiers of the high gain amplifier circuit from, for example,the first stage to the final stage.

According to the above means, even if a DC offset occurs with selfmixing of the mixer due to round intrusion of a local oscillation signalinto LNA input terminals, the low noise amplifier is brought to theoperating state to execute the offset cancel operation of thefinal-stage programmable gain amplifier where the high gain amplifiercircuit is operated with the high gain, whereby offsets can be canceledinclusive of the DC offset of the final-stage programmable gainamplifier and the DC offset produced with the self mixing of the mixer.Further, when the high gain amplifier circuit is operated with the lowgain, the low noise amplifier is brought to the non-operating state toexecute in sequence the offset cancel operations of all programmablegain amplifiers of the high gain amplifier circuit from the first stageto the final stage, thereby making it possible to prevent each DC offsetfrom increasing due to an interference wave inputted to the LNA andprevent the offset cancel operations from failing.

Here, preferably, a register is provided which sets gain reaching athreshold value for determining which one of the two offset canceloperations should be executed. Thus, the suitable offset canceloperation can be performed automatically by setting the optimumthreshold value according to a system to be applied.

Advantageous effects obtained by representative ones of the inventionsdisclosed in the present application will be explained in brief asfollows:

According to the present invention, a wireless communicationsemiconductor integrated circuit device (high frequency IC) of a directconversion system is capable of canceling a DC offset developed withself mixing of a mixer due to round intrusion of a local oscillationsignal into LNA input terminals. Therefore, even if the dynamic range ofa subsequent-stage circuit is narrow, it is possible to prevent adesired wave from being clipped and thereby improve receptionsensitivity.

According to the present invention as well, even if the amount of roundintrusion of a local oscillation signal into LNA input terminals variesaccording to a mounted substrate, a DC offset developed with self mixingcan be canceled. Therefore, it is possible to obtain a wirelesscommunication semiconductor integrated circuit device (high frequencyIC) of a direct conversion system which has stable reception sensitivitywithout being affected by the characteristic of the mounted substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an embodiment of a reception systemcircuit of a direct conversion system employed in a wirelesscommunication system of a cellular phone or the like suitable forapplication of the present invention;

FIG. 2 is a timing chart illustrating offset correction timings for afirst operation mode of PGA employed in the reception system circuitaccording to the embodiment and offset correction timings for a secondoperation mode thereof;

FIG. 3 is a block diagram showing a configurational example of a controlcircuit for controlling offset correction circuits employed in thereception system circuit according to the embodiment;

FIG. 4 is a flowchart showing a method of selecting an offset correctionfor the first operation mode of PGA employed in the reception systemcircuit according to the embodiment and an offset correction for thesecond operation mode thereof;

FIG. 5 is a flowchart showing another example of a method of selectingan offset correction for the first operation mode of PGA employed in thereception system circuit according to the embodiment and an offsetcorrection for the second operation mode thereof;

FIG. 6 is a circuit diagram illustrating a configurational example of anLNA (Low Noise Amplifier) employed in the reception system circuitaccording to the embodiment;

FIG. 7 is a circuit diagram showing a configurational example of a mixercircuit employed in the reception system circuit according to theembodiment; and

FIG. 8 is a block diagram showing a configurational example illustrativeof a high-frequency IC and a wireless communication system to which thereception system circuit according to the embodiment is applied.

DETAILED DESCRIPTION OF THE PREFFERED EMBODIMENTS

Preferred embodiments of the present invention will hereinafter bedescribed in detail with reference to the accompanying drawings.

A reception system circuit of a direct conversion system employed in awireless communication system of a cellular phone or the like suitablefor application of the present invention is shown in FIG. 1.

The reception system circuit according to the present embodimentcomprises an LNA (Low Noise Amplifier) 210 which amplifies a receivedsignal, an oscillator 250 which generates a local oscillation signalφRF, a mixer 212 which combines the received signal amplified by the LNA210 and the local oscillation signal φRF generated by the oscillator 250and down-converts the result of combination to a signal lying in anaudio frequency band, and a high gain amplifier circuit 220 whichamplifies the down-converted signal.

In the high gain amplifier circuit 220, a first variable gain amplifier(programmable gain amplifier) PGA1 is connected to a stage subsequent toa first low pass filter LPF1, a second low pass filter LPF2 is connectedto a stage subsequent to the programmable gain amplifier PGA1, and asecond programmable gain amplifier PGA2 is connected to a stagesubsequent to the second low pass filter LPF2. Further, a third low passfilter LPF3 is connected to a stage subsequent to the secondprogrammable gain amplifier PGA2, and a third programmable gainamplifier PGA3 is connected to a stage subsequent to the third low passfilter LPF3. Furthermore, a final amplifier FAMP capable of switchinggain to two stages is connected to a stage subsequent to the thirdprogrammable gain amplifier PGA3, and a fourth low pass filter LPF4 isconnected to a stage subsequent to the final amplifier FAMP. In thepresent embodiment, although not restricted in particular, a primaryfilter is used for the first low pass filter LPF1, and a secondaryfilter is used for the second through fourth low pass filters LPF2through LPF4. Thus, a relatively flat frequency characteristic isobtained as a whole, and an interference wave having a frequency 3 MHzaway from a receiving band can be reduced sufficiently.

Incidentally, the programmable gain amplifiers PGA1 through PGA3 areamplifiers capable of adjusting gain substantially linearly or in amultistage. The final amplifier FAMP is capable of making use of a fixedgain amplifier since the gain is uniquely determined if the type of abaseband circuit determined by the system, i.e., used therein isdecided. In the present embodiment, however, an amplifier capable ofswitching gain to two stages or so is used to enable the selection ofthe gain according to an adaptive system, thereby enhancing generalversatility of a high frequency LSI200.

In the reception system circuit according to the present embodiment, afirst offset correction circuit or corrector OFC1 is providedcorresponding to the first programmable gain amplifier PGA1, a secondoffset correction circuit or corrector OFC2 is provided corresponding tothe second programmable gain amplifier PGA2, and a third offsetcorrection circuit or corrector OFC3 is provided corresponding to thethird programmable gain amplifier PGA3. A control circuit 240, whichsequentially operates the offset correction circuits OFC1 through OFC3to carry out offset cancel processing and performs on/off-control of theLNA 210, is provided in association with the offset correction circuitsOFC1 through OFC3.

In the present embodiment, although not restricted in particular, theoffset correction of the first programmable gain amplifier PGA1 isexecuted inclusive of the mixer 212. Such a correction is performed asfollows: In a state in which, for example, the LNA 210 is turned off anddifferential input terminals of the mixer 212 are brought to the samepotential, the difference in level between output signals of the PGA1 atthat time, i.e., an offset voltage is detected by the offset correctioncircuit OFC1, and such a potential as to bring it to “0” is appliedbetween input terminals of the PGA1, whereby an offset cancel operationcan be performed more accurately.

As indicated by the first offset correction circuit OFC1 as arepresentative of the offset correction circuits OFC1 through OFC3, itcomprises an AD converter ADC1 which AD-converts the output of theamplifier PGA1, and a DA converter DAC1 which DA-converts a valueretained in each register provided within the control circuit 240 andadjusts the value of current flowing through a current source of theamplifier PGA1, or the like to thereby correct an offset. The registersREG1 through REG3, which hold offset correction values corresponding tothe offset correction circuits OFC1 through OFC3, are provided withinthe control circuit 240. On the basis of values obtained byAD-converting the differences in level between the output signals of theamplifiers by means of the AD converters ADC1 in a state in which theinput terminals of the respective amplifiers are respectively brought tothe same potential, such correction values as to bring the differences,i.e., offset voltages to “0” are determined and retained in theircorresponding registers. The determination of the correction values cansequentially be performed by comparative AD converting operations.

Further, the control circuit 240 is provided therewithin with a registerREG10 which holds data (gain code) used to specify or designate totalgain supplied from a baseband circuit 300 at the receiving operations ofthe programmable gain amplifiers PGA1 through PGA3, a decoder DEC whichdecodes the code set to the register REG10 to generate a code fordesignating gain of each of the amplifiers PGA1 through PGA3, registersREG11 through REG13 each of which retains the gain code generated by thedecoder DEC, a timing logic 241 which operates the offset correctioncircuits OFC1 through OFC3 with predetermined timing and generatestiming signals GC1 through GC3 for performing switching among the gainsof the programmable gain amplifiers PGA1 through PGA3 on the basis ofthe values retained in the registers REG11 through REG13, etc.

As shown in FIG. 2(A), the reception system circuit according to thepresent embodiment is configured so as to have a second operation mode(see FIG. 2(B)) for sequentially performing offset cancellations of theprogrammable gain amplifiers PGA1 (including the mixer), PGA2 and PGA3by the offset correction circuits OFC1, OFC2 and OFC3 while the LNA 210remains off in a manner similar to the conventional example, in additionto a first operation mode for sequentially performing the offsetcancellations of the programmable gain amplifiers PGA1 (including themixer) and PGA2 by the offset correction circuits OFC1 and OFC2 firstlyin a state in which the LNA 210 has been turned off, and thereafterperforming the offset cancellation of the programmable gain amplifierPGA3 by the offset correction circuit OFC3 in a state in which the LNA210 has been turned on. Incidentally, the offset cancel operations ofthe programmable gain amplifiers PGA1 through PGA3 are executed in astate in which the gains of the PGA1 through PGA3 have been set, in sucha manner that the total gain stet to the register REG10 from outside atthat time is obtained.

Further, in the reception system circuit according to the presentembodiment, a means or mechanism for automatically selecting any one ofthe first operation mode for performing the offset cancellation of theprogrammable gain amplifier PGA3 in the state in which the LNA 210 isbeing turned on when the gains set to the PGA1 through PGA3 are high,and the second operation mode for sequentially performing the offsetcancellations of the programmable gain amplifiers PGA1 through PGA3while the LNA 210 remains off when the gains set to the PGAs are low,thereby to carry out at least one offset cancellation, and a means ormechanism for carrying out the offset cancellations in either the firstoperation mode or the second operation mode according to a designationgiven from outside are provided in the control circuit 240.

As shown in FIG. 3, the mechanism for automatically selecting either thefirst operation mode or the second operation mode according to the setgains comprises a threshold register REG21 which sets a threshold valueupon mode selection, a comparator CMP which compares the set value ofthe threshold register REG21 and a set value (total gain) of a gaindesignation register REG10, etc. The setting of the threshold registerREG21 is performed once at power-on. The setting of the gain designationregister REG10 is performed corresponding to a received level uponstating of a reception mode. The threshold value to be set is determineddepending on, for example, how much the level is necessary for abaseband circuit to be used, as an input signal. The timing logic 241generates and outputs such timing signals as to execute offsetcancellations in the first operation mode when the gains set to the PGA1through PGA3 are higher than the threshold value and in the secondoperation mode when the gains set to the PGA1 through PGA3 are lowerthan the threshold value, respectively, in accordance with the result ofcomparison by the comparator CMP.

Here, the reason why the offset cancellations are respectively executedin the first operation mode when the gains set to the PGA1 through PGA3are higher than the threshold value and in the second operation modewhen the gains set to the PGA1 through PGA3 are lower than the thresholdvalue, is that although the low pass filters LPF1 through LPF3 arecapable of sufficiently reducing the interference wave having thefrequency 3 MHz away from the receiving band, they are not capable ofsufficiently reducing an interference wave a few hundred kHz awaytherefrom.

Described specifically, even if the interference wave of 3 MHz isinputted from the LNA upon execution of the offset cancellations andamplified by PGA1 and PGA2 where the gains set to the PGA1 through PGA3are high, i.e., where a signal level at an antenna end is small, it isattenuated to such an extent that no interference occurs in the low passfilters LPF1 through LPF3. Since, however, the low pass filters LPF1through LPF3 are not capable of sufficiently reducing an interferencewave of a few hundred kHz, the interference wave of the few hundred kHzis amplified in the second operation mode for canceling the offsets ofall the programmable gain amplifiers PGA1 through PGA3 in the turn-offstate of the LNA 210 when the LNA is turned on after completion of theoffset cancellations, and inputted to the PGA3 without being subjectedto attenuation sufficiently. Therefore, when pairing with a stage priorto the input terminals of the LNA 210 is poor, a DC offset caused by theinterference wave appears, and when an interference wave contained in asignal inputted to the PGA3 is large, the input signal of the ADconverter changes during the operation of each offset correction circuitand hence the offset cancel operation per se will fail. Thus, when thegain set to the PGA is higher than the threshold value, the offsetcancellation of the programmable gain amplifier PGA3 is performed in thestate in which the LNA 210 has been turned on. Consequently, the firstoperation mode for performing the offset cancellations inclusive of theDC offset of the LNA becomes effective.

On the other hand, when the gains set to the PGA1 through PGA3 are low,i.e., the signal level at the antenna end is high, a shift in PGA outputdeveloped upon execution of cancellation in a state in which the LNA 210is turned on and the interference wave of the few hundred kHzsufficiently non-attenuated by the low pass filters LPF1 through LPF3 isamplified by PGA1 and PGA2 and inputted to the PGA3, becomes larger thana shift in PGA output due to a DC offset developed by self-mixing of themixer with round intrusion of the local oscillation signal into the LNAinput terminals when the LNA is turned off and the LNA is turned onafter the offset cancellations of PGA1 through PGA3. Therefore, when thegains set to the PGAs are low, the second operation mode forsequentially performing the offset cancellations of the programmablegain amplifiers PGA1 through PGA3 while the LNA 210 remains off, becomeseffective.

As shown in FIG. 4, the timing logic 241, which generates an on/offcontrol signal Rx_fon and timing signals T1 through Tn relative to theoffset correction circuits OFC1 through OFC3 for PGA1 through PGA3,compares the set value of the threshold register REG21 and the totalgain of PGAs after the setting of the total gain of PGAs from theoutside (baseband LSI) to the register REG10, and generates such timingsignals as to execute the offset cancellation based on the firstoperation mode for turning on the LNA in mid course when the PGA gain islower than the threshold value and to execute the offset cancellationbased on the second operation mode for causing the LNA to remain offwhen the PGA gain is higher than the threshold value.

On the other hand, the mechanism for allowing execution of the offsetcancellations in either the first operation mode or the second operationmode in accordance with the external designation is enabled by provisionof a register (hereinafter called CT register) REG22 which designatesthe operation mode as shown in FIG. 3. The setting of the CT registerREG22 is performed upon starting of a reception mode. The CT registerREG22 is not limited to one comprising plural bits but may be oneconfigured of a one-bit flag. A bit for designating the operation modeand a bit indicative of whether the setting of the correspondingregister is valid or invalid, can be provided in the CT register REG22.

When the setting to the CT register REG22 is carried out as shown inFIG. 5, the timing logic 241 generates such a timing signal as to carryout an offset cancellation based on the first operation mode or anoffset cancellation based on the second operation mode according to theset state of the CT register REG22.

Incidentally, the timing logic 241 may be configured in such a way as togenerate such a timing signal that when the setting to the thresholdregister REG21 has been made, the set value of the threshold registerREG21 and the total gain of PGAs are compared based on the set state ofthe threshold register REG21 to thereby carry out the offsetcancellation based on the first operation mode or the second operationmode and to generate such a timing signal as to allow the execution ofthe offset cancellation based on the first operation mode or the secondoperation mode according to the set state of the CT register REG22.

A specific circuit example of the LNA (Low Nose Amplifier) 210 is shownin FIG. 6. The LNA according to the present embodiment comprises a pairof differential input transistors Q1 and Q2 of which the emitters areconnected in common and the base terminals are connected to theircorresponding input terminals IN1 and IN2 of received signals, loadresistors R1 and R2 respectively connected between the collectors of thetransistors Q1 and Q2 and a power supply voltage Vcc, bias transistorsQ3 and Q4 of which the base terminals are respectively connected to thebase terminals of the transistors Q1 and Q2 via resistors R3, R4, R5 andR6, constant current sources CI1 and CI2 respectively connected betweenthe collectors of the transistors Q3 and Q4 and the power supply voltageVcc, and switches SW1 and SW2 connected in series with the constantcurrent sources CI1 and CI2 respectively. When the switches SW1 and SW2are on/off controlled by the control signal Rx_fon supplied from thecontrol circuit 240, the circuit is brought to an operating state or anon-operating state.

The transistors Q3 and Q4 have collector terminals connected to aconnecting node N1 of the resistors R3 and R4 and a connecting node N2of the resistors R5 and R6 respectively and constitute a current mirrorcircuit together with the differential input transistors Q1 and Q2. Whenthe switches SW1 and SW2 are respectively brought to an on state,predetermined bias voltages are respectively applied to the bases of thedifferential input transistors Q1 and Q2 to amplify the signals inputtedto the input terminals IN1 and IN2. When the switches SW1 and SW2 arerespectively brought to an off state, collector currents that flowthrough the transistors Q3 and Q4 are cut off so that the bases of thedifferential input transistors Q1 and Q2 are clamped to the neighborhoodof a ground potential. Therefore, the circuit is brought to anon-operating state in which even if the signals inputted to the inputterminals IN1 and IN2 change, the output voltages of the collectors ofthe transistors Q1 and Q2, i.e., the LNA remain substantially unchanged.

A specific circuit example of the mixer 212 is shown in FIG. 7. Themixer according to the present embodiment comprises two sets of inputdifferential transistor pairs Q11 and Q12, and Q1 and Q22 of which theemitters are respectively connected in common, a differential transistorpair Q31 and Q32 of which the collectors are respectively connected tothe common emitters of these transistor pairs and the emitters areconnected to each other, and both of which are operated like currentswitches, a constant current source IC10 connected to the commonemitters of the transistor pair Q31 and Q32, and collector resistors Rc1and Rc2 respectively connected between the collectors of the inputdifferential transistors Q11 and Q21 and a power supply voltage Vcc andbetween the collectors of the transistors Q12 and Q22 and the powersupply voltage Vcc. A low pass filter LPF1 comprising resistors R11 andR12 connected in series with their corresponding output signal lines,and a capacitor C10 connected between the output signal lines isconnected to the output terminals of the mixer.

In the mixer 212 according to the present embodiment, the receivedsignal φRX amplified by the LNA 210 and its inverted signal /φRX areinputted to the base terminals of the two sets of input differentialtransistor pairs Q11 and Q12, and Q21 and Q22. The high frequencyoscillation signals φRF and /φRF generated by the RFVCO 250 are inputtedto the base terminals of the transistor pair Q31 and Q32. Thus, a signalobtained by combining the received signal φRX and the high frequencysignal φRF is outputted from each of output nodes N11 and N12. Thesignal is passed through the low pass filter LPF1 so that a highfrequency component is eliminated. Thus, a signal having a frequencyequal to the difference in frequency between the received signal φRX andthe high frequency signal φRF produced from the RFVCO is supplied to thesubsequent PGA.

A configurational example of a high frequency IC (RF-IC) and a wirelesscommunication system to which the reception system circuit of the directconversion system according to the embodiment of FIG. 1 is applied, willnext be explained using FIG. 8.

As shown in FIG. 8, the wireless communication system according to theembodiment comprises an antenna 400 for transmitting and receiving asignal wave, a transmit-receive switching means 410 comprising achangeover switch or a duplexer (branching filter), single-differentialconverters 420 a through 420 d each of which converts a single-phasereceived signal to a differential signal, a high frequency poweramplifier circuit (power module) 430 which amplifies a transmit signal,a high frequency IC 200 which demodulates the received signal andmodulates the transmit signal, a baseband circuit 300 which performsbaseband processing such as conversion of transmit data into I and Qsignals, extraction of receive data from the demodulated I and Qsignals, etc. and controls the high frequency IC 200, etc. In thepresent embodiment, the high frequency IC 200 and the baseband circuit300 are respectively configured over discrete semiconductor chips as asemiconductor integrated circuit device.

Although not restricted in particular, the high frequency IC 200according to the present embodiment is configured so as to be capable ofmodulating and demodulating signals lying in four frequency bands, basedon the communication systems of GSM850, GSM900, DCS1800 and PCS1900. Thefour single-differential converters 420 a through 420 d are providedcorrespondingly. When a simple changeover switch is used as thetransmit-receive switching means 410, the single-differential converters420 a through 420 d may share the functions of bandpass filters.

The high frequency IC 200 according to the present embodiment comprisesa reception system circuit RXC, a transmission system circuit TXC, and acontrol system circuit comprising circuits common to the transmissionsystem circuit, such as a control circuit, a clock generator, etc. otherthan those if roughly divided.

The reception system circuit RXC comprises low noise amplifiers 210 athrough 210 d which respectively amplify received signals lying in therespective frequency bands of GSM850, GSM900, DCS1800 and PCS1900, adivision phase shift circuit 211 which divides a local oscillationsignal φRF generated by a high frequency oscillator (RFVCO) 250 andthereby generates quadrature signals phase-shifted 90° from each other,mixers 212 a and 212 b which mix the quadrature signals generated by thedivision phase shift circuit 211 into the received signals amplified bythe low noise amplifiers 210 a through 210 d to thereby carry outdemodulation and down-conversion of I and Q signals, high gain amplifiersections 220A and 220B common to the respective frequency bands, whichrespectively amplify the demodulated I and Q signals and output them tothe baseband LSI 300, an offset cancel circuit 213 for canceling out DCoffsets of amplifiers lying within the high gain amplifier sections 220Aand 220B, etc.

The high gain amplifier section 220A has a configuration wherein aplurality of low pass filters LPF11, LPF12, LPF13 and LPF14 andprogrammable gain amplifiers PGA11, PGA12 and PGA13 are alternatelyconnected in a series configuration with one another and an amplifierAMP1 whose gain is fixed is connected to the final stage. The high gainamplifier section 220A amplifies the demodulated I signal to apredetermined amplitude level while removing an unnecessary wave.Similarly, the high gain amplifier section 220B also has a configurationin which a plurality of low pass filters LPF21, LPF22, LPF23 and LPF24and programmable gain amplifiers PGA21, PGA22 and PGA23 are alternatelyconnected in a series configuration with one another and an amplifierAMP2 whose gain is fixed is connected to the final stage. The high gainamplifier section 220B amplifies the demodulated Q signal to apredetermined amplitude level.

The circuit shown in FIG. 1 is used as the offset cancel circuit 213.That is, the offset cancel circuit 213 comprises offset correctioncircuits OFC1 through OFC3 comprising A/D converters (ADC) and D/Aconverters (DAC) provided in association with the programmable gainamplifiers PGA1 1 through PGA13 and PGA21 through PGA23, and a controlcircuit 240 which controls these offset correction circuits to allowthem to carry out offset cancel operations thereof.

The transmission system circuit TXC comprises an oscillator (IFVCO) 230which generates an oscillation signal φIF having an intermediatefrequency like, for example, 640 MHz, a division phase shift circuit 232which divides the oscillation signal φIF generated by the oscillator 230and thereby generates quadrature signals phase-shifted 900 from eachother, modulators 233 a and 233 b respectively configured of mixerswhich modulate the generated quadrature signals on the basis of the Isignal and Q signal supplied from the baseband circuit 300, an adder 234which combines the modulated signals, transmission oscillators (TXVCO)240 a and 240 b each of which generates a transmit signal φTX having apredetermined frequency, an offset mixer 235 which combines a feedbacksignal obtained by extracting the transmit signal φTX outputted fromeach of the transmission oscillators 240 a and 240 b by means of acoupler or the like and a signal φRF′ obtained by dividing theoscillation signal φRF generated by the high frequency oscillator(RFVCO) 250 to thereby generate a signal having a frequency equivalentto the difference in frequency therebetween, a phase comparator 236which compares the output of the offset mixer 235 and the signal TXIFcombined by the adder 234 to thereby detect a difference in frequencyand a difference in phase, a charge pump and loop filter 237 whichgenerates a voltage corresponding to the output of the phase comparator236, buffer circuits 238 a and 238 b which convert the differentialoutputs of the TXVCOs 240 a and 240 b into single signals and output thesame therefrom, etc.

One of the transmission oscillators 240 a and 240 b is a circuit whichgenerates a transmit signal lying in an 850 to 950 MHz band for GSM,whereas the other thereof is a circuit which generates a transmit signallying in a 1800 to 1900 MHz band for DCS and PCS.

A control logic or control circuit 260 which controls the whole chip, anRF synthesizer 261 which constitutes a PLL circuit for RF together withthe high frequency oscillator (RFVCO) 250, an IF synthesizer 262 whichconstitutes a PLL circuit for IF together with the intermediatefrequency oscillator (IFVCO) 230, and a reference oscillator (DCXO) 264which generates a clock signal φref used as a reference signal for thesesynthesizers 261 and 262, are provided over the chip for the highfrequency IC 200 according to the present embodiment. The synthesizers261 and 262 comprise phase comparators, charge pumps, loop filters, etc.respectively.

Incidentally, since the reference oscillation signal φref needs highfrequency accuracy, an external crystal oscillator is connected to thereference oscillator 264. A frequency like 26 MHz or 13 MHz is selectedas the reference oscillation signal φref. This is because the crystaloscillator with such a frequency is a general purpose part and is easilyavailable.

The control circuit 260 is provided with a control register to whichsettings are made based on signals from the baseband IC 300. Describedspecifically, a synchronizing clock signal CLK, a data signal SDATA anda load enable signal LEN used as a control signal are supplied from thebaseband IC 300 to the high frequency IC 200. When the load enablesignal LEN is asserted effective in level, the control circuit 260sequentially takes in is the data signal SDATA transmitted from thebaseband IC 300 in sync with the clock CLK and sets the same to thecontrol register.

Although not restricted in particular, the data signal SDATA is seriallytransmitted. The baseband IC 300 is configured of a microprocessor orthe like. The data signal SDATA contains commands to be supplied fromthe baseband IC 300 to the high frequency IC 200. The baseband IC 300determines gain at each of the high gain amplifier sections 220A and220B according to the level of the received signal and sends a code fordesignating the gain to the control circuit 260 of the high frequency IC200. The control circuit 260 transmits the received gain designationcode to the offset cancel circuit 213 as it is or decodes it and sendsit to the offset cancel circuit 213.

The offset canceling control circuit 240 shown in FIG. 1 may beconfigured as part of the control circuit 260 which controls the entirechip. Alternatively, the control circuit 240 is configured as a circuitseparate from the control circuit 260 and may be provided in the offsetcancel circuit 213. Even in the case where the control circuit isconfigured as a discrete circuit, the register REG10 which sets thetotal gain of PGAs and the decoder DEC both contained in the controlcircuit 240 shown in FIG. 1 may be provided on the side of the controlcircuit 260. The registers REG21 and REG22 shown in FIG. 3 may similarlybe provided on the side of either the control circuit 240 or 26.

In the wireless communication system of the multiband mode according tothe present embodiment, the control circuit 260 changes the frequency ofthe oscillation signal of the high frequency oscillator 250 according toa channel to be used, upon transmission/reception in accordance with acommand from the baseband IC 300, for example, and changes the frequencyof the signal supplied to the offset mixer 235 in accordance with a GSMmode or DCS/PCS mode to thereby perform switching of a transmitfrequency. Described specifically, the oscillation signal φRF of thehigh frequency oscillator 250 is supplied to the division phase shiftcircuit 211 as it is in a reception mode in the case of DCS and PCS. Inthe case of GSM, the oscillation signal φRF of the high frequencyoscillator 250 is divided into ½ by DVD1, which in turn is supplied tothe division phase shift circuit 211.

The oscillation frequency of the high frequency oscillator (RFVCO) 250is set to a value different from one in the reception mode in atransmission mode. The oscillation frequency fRF of the high frequencyoscillator (RFVCO) 250 in the transmission mode is set to, for example,3616 to 3716 MHz in the case of GSM850, 3840 to 3980 MHz in the case ofGSM900, 3610 to 3730 MHz in the case of DCS and 3860 to 3980 MHz in thecase of PCS. The signal φRF having such an oscillation frequency isdivided into ¼ by the corresponding divider in the case of GSM anddivided into ½ in the case of DCS and PCS, which in turn is supplied tothe offset mixer 235.

The offset mixer 235 outputs a signal equivalent to the difference(fRF−fTX) in frequency between the oscillation signal φRF outputted fromthe RFVCO 250 and the transmit oscillation signal φTX outputted fromeach of the transmission oscillators (TXVCO) TXVCOs 240 a and 240 b. Atransmission PLL (TXPLL) is operated in such a manner that the frequencyof the difference signal coincides with the frequency of the modulationsignal TXIF. In other words, the TXVCOs 240 a and 240 b are controlledso as to oscillate with the frequency equivalent to the differencebetween the frequency (fRF/4 in the case of GSM and fRF/2 in the case ofDCS and PCS) of the oscillation signal φRF outputted from the RFVCO 250and the frequency of the modulation signal TXIF.

While the invention made above by the present inventors has beendescribed specifically based on the embodiments, the present inventionis not limited to the above embodiments. It is needless to say thatvarious changes can be made thereto within the scope not departing fromthe gist thereof. Although the high gain amplifier circuit 220 comprisesthe three programmable gain amplifiers and one fixed gain amplifier inthe embodiment, for example, the present invention is applicable even toa reception system circuit having a high gain amplifier circuit free ofthe fixed gain amplifier, a high gain amplifier circuit comprising twoprogrammable gain amplifiers and one fixed gain amplifier, and a highgain amplifier circuit having four or more programmable gain amplifiers.Although the reception system circuit and the transmission systemcircuit are formed in one semiconductor chip in the high frequency ICaccording to the embodiment, they may be formed on discretesemiconductor chips respectively.

Although the respective offset correction circuits OFC1 through OFC3provided corresponding to the programmable gain amplifiers PGA1 throughPGA3 are respectively provided with the AD converters and the DAconverters in the embodiment, the offset correction circuits OFC1through OFC3 may be configured in such a manner that DA converters arerespectively provided therein, and an AD converter is provided as acommon circuit and changed over by a switch and used on a time-sharingbasis to thereby correct offsets.

Further, although the threshold register REG21 for setting the thresholdvalue to be compared with the gain set to the gain designation registerREG10 upon mode selection is provided in the embodiment, the thresholdvalue is fixed without providing the threshold register REG21, and thefixed threshold value and the gain set to the gain designation registerREG10 may be compared upon mode selection to determine whether an offsetcancel operation should be done in either the first operation mode orthe second operation mode.

While the above description has principally been made of the case inwhich the invention made by the present inventors is applied to a highfrequency IC employed in a cellular phone which belongs to the field ofapplication reaching the background of the invention, the presentinvention is not limited to it. The present invention can be widelyapplied to a general semiconductor integrated circuit device having areception system circuit that constitutes a wireless communicationsystem.

1. A wireless communication system comprising: an antenna whichtransmits and receives a signal wave; transmit-receive switching meanswhich supplies a transmission signal output from a transmission circuitto an antenna and supplies a reception signal received at the antenna toa reception circuit; single differential converters which converts thereception signal from the transmit-receive switching means into adifferential signal; and a baseband circuit which performs basebandprocessing on the transmission signal and reception signal, wherein thereception circuit including: a low noise amplifier circuit whichamplifies the differential signal, a mixer which synthesize an output ofthe low noise amplifier circuit and an oscillation signal having apredetermined frequency, and a high gain amplifier circuit whichincludes a plurality of programmable gain amplifiers and a plurality offilters are alternately connected in series, wherein the low noiseamplifier circuit is brought to a non-operating state to allow executionof an offset cancel operation of the programmable gain amplifier on thepre-stage side of the high gain amplifier circuit, and thereafter thelow noise amplifier circuit is brought to an operating state to allowexecution of an offset cancel operation of the programmable gainamplifier corresponding to a final stage, wherein reception circuitfurther comprising: a register or control bit capable of setting whetheror not the offset cancel operation for the pre-stage side of theprogrammable gain amplifier and the offset cancel operation for thefinal stage of the programmable gain amplifier, and wherein a value setto the register or the control bit is supplied from the baseband circuitto the reception circuit.
 2. A wireless communication system accordingto claim 1, wherein the reception circuit further comprising: an offsetcancel circuit which includes offset collection circuits provided inassociation with the programmable gain amplifiers and a control circuitwhich receives the value from the baseband circuit and controls theoffset collection circuits, wherein the register or the control bit areincluded in the control circuit.
 3. A wireless communication systemaccording to claim 2, wherein the transmission circuit and the receptioncircuit are formed on a high frequency integrated circuit device, andwherein the baseband circuit and the high frequency integrated circuitdevice are respectively formed on a semiconductor integrated circuitdevice.
 4. A wireless communication system according to claim 2, whereinthe threshold value for determining which one of the two offset canceloperations is executed, is a fixed value.
 5. A wireless communicationsystem according to claim 4, wherein the first gain is higher than thesecond gain.